Measurement method and device for performing the measurement method

ABSTRACT

The present invention relates to a measurement method in which, by predetermined illumination by means of a display device, in particular a holographic or autostereoscopic display device, with an intensity distribution of the illumination light in a plane of a light source image, a first location of an object, in particular an observer of the display device, is marked, and wherein the relative position of the first location in relation to a second location of the object is determined in a coordinate system of a camera.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of PCT/EP2012/074289, filed on Dec.3, 2012, which claims priority to German Application No. 10 2011 055967.1, filed Dec. 2, 2011, the entire contents of each of which areincorporated fully herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a measurement method and to anapparatus for carrying out the measurement method.

Display devices which allow observers a genuine spatial, i.e.three-dimensional, perception are becoming ever more popular.

Typically, observers of these display devices require auxiliary means,for example head-mounted displays, lamps, polarization glasses orshutter glasses, in order to be able to three-dimensionally perceive thescenes displayed by the display devices.

Display devices which allow the observers observation without additionalauxiliary means are also known. Typically, for these display devices,for example autostereoscopic display devices or holographic displaydevices, information is required regarding where the observer orobservers are situated in relation to the display device.

Conventionally, for this purpose, two cameras which record the space infront of the display device are used. Evaluation units connected to thecameras recognize the face of an observer of the display device and can,in particular, determine the position of the eye pupils of the observerin relation to the position of the cameras. The recording direction ofthe cameras in relation to the display device is in this casepredetermined in a fixed way, so that the position of the eye pupils inrelation to the display device can be determined from the position ofthe eye pupils in relation to the cameras. During transport of theapparatus, it may occur that the position and in particular theorientation of the camera in relation to the display device is altered.Thus, the position of the eye pupils in relation to the display devicecan no longer be determined accurately, or correctly, and recalibrationof the device is necessary.

Furthermore, special apparatuses with which objects can be measuredthree-dimensionally are known. Typically, in the case of theseapparatuses, lines are generated on the object with a laser. Images ofthe object illuminated with these lines are then recorded with a cameraand the shape of the object is calculated from the distortion of thelines and stored as a digital model. In order to provide an observerwith the possibility of examining this digital model, however, anotherdigital display device is additionally necessary.

Against this background, it was consequently the object of the inventionto provide a measurement method and an apparatus having reducedequipment outlay.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved by thesubject-matter of independent patent claims 1 and 15. Advantageousconfigurations of the invention are mentioned in patent claims 2 to 14and 16 to 18 referring back to patent claims 1 and 15.

Thus, the solution to the object consists in a measurement method,wherein by predetermined illumination by means of a display device, withan intensity distribution of the illumination light in a plane of alight source image, a first location of an object, is marked, andwherein the relative position of the first location in relation to asecond location of the object is determined in a coordinate system of acamera.

The invention is based on the concept that the display device itself isused as a means for determining the relative position of the firstlocation of the object in relation to a second location of the object.Since the illumination for the display of image information ispredetermined by the display device itself, it is possible to determinethe position of the first location of the object and, by means of therelative position of the second location in relation to the firstlocation in the coordinate system of the camera, also the position ofthe second location of the object in the coordinate system of thedisplay device.

Calibration of the camera, that is to say determination of its positionand orientation, in relation to the coordinate system of the displaydevice can therefore be dispensed with.

By using a holographic display device, the intensity distribution of theillumination light in the plane of the light source image can begenerated by constructive or destructive interference of coherent lightbeams. In this way, an intensity distribution of the illumination lightvarying strongly with the distance of the object from the display devicecan be achieved in a controlled way.

An autostereoscopic display device can be composed of simpler modulesthan a holographic display device. In particular, autostereoscopicdisplay devices do not require light sources that generate light with alarge coherence length, in order to represent three-dimensional scenes.The use of an autostereoscopic display device can therefore make themethod simpler.

The marking of the first location of an observer of the display devicemay above all be advantageous when the display device is intended tointeract with the observer. It is, however, also conceivable to mark thefirst location of an inanimate object so that it can be measured, or canbe deliberately illuminated with a texture.

According to a first refinement of the measurement method, the intensitydistribution of the illumination light in the plane of the light sourceimage comprises a light source image of a diffraction order.

Display devices typically have a spatial modulator for light with apredetermined raster. The raster of the spatial modulator can be used asa natural diffraction grating with a predetermined grating period, sothat the intensity distribution of the illumination light in the planeof the light source image may comprise a light source image of adiffraction order. It is conceivable to use the light source image ofthe 0^(th) diffraction order, that is to say undiffracted light sourceimage. It is, however, also possible to use higher diffraction orders. Aplurality of diffraction orders may also be used for generating theintensity distribution, for example in order to increase the precisionof the measurement method, since a plurality of light source images canbe detected. Owing to the predetermined grating period, the spacings ofthe maxima and/or minima in the intensity distribution can bepredetermined very accurately. It is possible to predetermine theaccuracy of the determination of the relative position of the firstlocation in relation to the second location very accurately.

According to another configuration of the measurement method, the secondlocation is an eye pupil of the observer, and the relative position ofthe first location in relation to the eye pupil of the observer isdetermined in the coordinate system of the camera. The eye pupils of theobserver are very conspicuous points or regions on the face of theobserver. They can therefore be recognized relatively simply byevaluation logic connected to the camera. Furthermore, the determinationof the relative position of the first location in relation to theposition of an eye pupil of the observer can make control possible as afunction of the eye pupil position of the observer. In particular,observers who cannot otherwise be distinguished on physical grounds canbenefit from this.

Furthermore, according to an exemplary embodiment of the measurementmethod, the first location is brought to coincide with a predeterminableregion of the face of the observer, in particular with the eye pupil ofthe observer, by variation of the predetermined illumination. In thisway, observer tracking can be carried out.

In the case of display devices which are intended to allow the observersgenuine three-dimensional perception without auxiliary means, forexample polarization glasses or shutter glasses, it may be advantageousnot only to determine the relative position of the first location inrelation to the second location, but to bring them directly to coincide.In this way, it can become possible to deliberately illuminate only apredeterminable region of the face of the observer when playing filmscenes, for example. In this way, the computation outlay for thecalculation of the three-dimensional representation can be reduced.

According to another refinement of the measurement method, an image tobe displayed to the observer is used as the intensity distribution ofthe illumination light in a plane of a light source image or as a lightsource image.

The use of the image to be displayed to the observer can make itpossible to carry out the measurement method even when it is used as adisplay device for the observer. When a display device representingthree-dimensional scenes is involved, the representation may be adaptedto a varying position of the observer.

According to another configuration of the measurement method, the secondlocation of the object is defined by predetermined illumination by meansof the display device with a second intensity distribution of theillumination light in a plane of a second light source image.

The distance between the first location of the object and the secondlocation can in this way be known in the coordinate system of thedisplay device, and the position and orientation of the camera inrelation to the display device can therefore be determined from therelative distance of the first location in relation to the secondlocation in the coordinate system of the camera.

The second intensity distribution of the illumination light in the planeof the second light source image may have a light source image of adiffraction order. The use of diffraction orders as light source imagescan have the advantage that their distances, or the underlyingdiffraction angles, can be predetermined in a fixed way by a raster ofthe display device. The reproducibility of the method can therefore beimproved.

Furthermore, according to an exemplary embodiment of the measurementmethod, a predeterminable pattern is formed on the object, in particularthe face of the observer, with the first and second intensitydistributions of the illumination light, an image of the pattern isrecorded with the camera, and the recorded image of the pattern isexamined for differences from the predeterminable pattern.

By determining the differences from the predeterminable pattern, it isconceivable to determine the shape of the object. It may also bepossible to determine whether the object corresponds to a predeterminedobject or to a different object.

According to another refinement of the measurement method, a firstdiffraction order is used as the first light source image and adifferent diffraction order is used as the second light source image.

The use of defined diffraction orders as light source images can havethe advantage that their distance can be predetermined in a fixed way bya raster of the display device, so that the measured relative positionscan be attributed to absolute positions. The diffraction pattern isgiven by the raster of the display device, or of a controllable spatiallight modulator of the display device, the wavelength of the light used,or the wavelengths used, and the distance to the illuminated plane, i.e.the distance to the illuminated object.

According to another configuration of the measurement method, acalibrated object is used. A calibrated object is intended to mean anobject having a sufficiently accurately known shape. From thedetermination of the relative position of the first location of theobject in relation to the second location of the calibrated object inthe coordinate system of the camera, the position and orientation of thecamera can be determined with improved accuracy in relation to thecoordinate system of the display device.

Furthermore, according to an exemplary embodiment of the measurementmethod, the coordinate system of the camera is calibrated in relation toa coordinate system of the display device from the relative position ofthe first location in relation to the second location in the coordinatesystem of the camera.

The calibration of the coordinate system of the camera can make itpossible to obviate continuous determination of the relative position,since the position of the second location of the object in thecoordinate system of the display device can also be determined withouthaving to mark a first location of the object by predeterminedillumination. Calibration is only necessary at relatively largedistances, when the orientation and/or position of the camera have beenaltered. Calibration may, in particular, be necessary after transport ofthe apparatus. It is conceivable to carry out the calibration atpredetermined time intervals. It may, however, also be envisioned tocarry out the calibration only in response to explicit requirement bythe observer.

According to another refinement of the measurement method, the camera isarranged at a predetermined distance and/or in a predeterminedorientation with respect to the display device, and the position of thesecond location in a coordinate system of the display device isdetermined from the relative position of the first location in relationto the second location in the coordinate system of the camera. In thisway, in particular, the shape of the object can be determined.

According to another configuration of the measurement method, the firstlight source image and the second light source image is generated by anoptical system of the display device and by predetermined illuminationof a controllable spatial light modulator with light of a first visiblewavelength and/or a second visible wavelength and/or a third visiblewavelength and/or an infrared wavelength, and the camera and/or afurther camera is provided with a filter which is transmissiveessentially only for light of the first visible wavelength and/or thesecond visible wavelength and/or the third visible wavelength and/orinfrared wavelength.

By the use of light of a defined wavelength and of a correspondingfilter, the signal-to-noise ratio can be improved. In particular, aninfluence of ambient light on the measurement result can be reduced. Theuse of a filter which is transmissive for light of infrared wavelengthcan be advantageous, in particular, when recording the observer. Forexample, the position of the eye pupils of the observer may possibly besimpler to determine when the filter of the camera transmits only lightof infrared wavelength.

Typically, with display devices of the type described here, theobservers are shown colored light source images which are formed bylight of three wavelengths. By the use of all three wavelengths, theaccuracy of the measurements can be improved.

Furthermore, according to another exemplary embodiment of themeasurement method, the relative position of the first location inrelation to the second location is determined in a second coordinatesystem of a second camera.

By the use of a second camera, in addition to information about thedirections in which the first location of the object and the secondlocation of the object lie, it is also possible to obtain informationabout the distance of the first and second objects from the displaydevice. Further cameras may possibly further improve the spatialresolution.

According to another exemplary embodiment of the measurement method, bypredetermined illumination by means of a display device, in particular aholographic or autostereoscopic display device, with an intensitydistribution of the illumination light in a plane of a light sourceimage, a first location of an observer of the display device is marked,a viewing window of an image to be displayed to the observer is used asthe intensity distribution of the illumination light in a plane of alight source image or as a light source image, the relative position ofthe first location in relation to the eye pupil of the observer isdetermined in the coordinate system of the camera, and the firstlocation is brought to coincide with a predeterminable region of theface of the observer, in particular with the eye pupil of the observer,by variation of the predetermined illumination. The measurement methodmay be carried out for both eye pupils. The observer may be providedwith specific image information for each eye pupil. In this way, forexample, a particularly good depth impression can be imparted.Furthermore, the viewing window may be tracked continuously to theposition of the eyes, so that it is possible to avoid light images ofhigher diffraction orders from being picked up by the eye pupils.

On the other hand, the object mentioned above is achieved by anapparatus for carrying out the measurement method, wherein the apparatuscomprises a display device, a camera and an evaluation unit fordetermining the position of the first location in a coordinate system ofthe camera.

The advantages associated with such a display device, in particular witha holographic display device or an autostereoscopic display device, havealready been described above in relation to the method according to theinvention.

According to a first refinement of the apparatus, the camera comprises aCCD sensor.

CCD sensors can have a particularly large dynamic range, that is to sayrecord both very bright and very dark regions of the image region.

As an alternative, the camera may also comprise a CMOS sensor. Ingeneral, CMOS sensors have a larger dynamic range than CCD sensors, CCDsensors generally having a higher bit depth in comparison with CMOSsensors. CMOS sensors can typically also record long-wavelength infraredlight.

The camera could also be a color camera. By the additional use of colorinformation, the accuracy of the relative position determination can beimproved further.

Furthermore, according to an exemplary embodiment of the apparatus, theapparatus comprises a light source and an optical system, and anintensity distribution of the illumination light in a plane of a lightsource image can be generated with the light source and the opticalsystem.

According to the present invention, with the aid of an intensitydistribution of the illumination light imaged or projected onto anobject, a reliable relative position of the first location of the objectto a second location of the object can be determined in a coordinatesystem of a camera, the second location being the eye pupil of theobserver.

So that the signal-to-noise ratio can be increased, according to apreferred embodiment at least one narrow bandpass filter could be used.The transmission characteristic of a triple bandpass filter is shown inFIG. 5 . In this case, the transmission is plotted as a function of thewavelength of the light used. The transmission can be optimized in sucha way that it respectively acts for a plurality of narrowband spectralranges. Accordingly, it is possible to use corresponding spectralwindows for example for (457±3) nm, (532±3) nm, (640±3) nm and/or(780±5) nm. Such spectral filters are now already mass products, themain field of use of which is in fluorescence light microscopy or incolor-separated three-dimensional representation of objects. It is alsopossible to use merely one infrared wavelength, for example 780 nm, inorder to be employed as an invisible component. This is because lightwith a wavelength of 780 nm can only be seen with high intensities. Itis thus possible to use a narrow spectral window in the near-infraredrange or in the infrared range. The ambient light can be suppressed by afactor of, for example, >200.

Advantageously, it is furthermore possible, for example, to use infraredline scanning (i.e. a line raster) with the use of an additionalsubsystem of the measurement method according to the invention.

The detection or determination of the eye position may be carried outwith the aid of a CMOS array or a CMOS line. A retina scan in this caseconstitutes a rapid possibility for tracking the eye position. This maybe implemented with the use of a near-infrared LED, which produces apredetermined spatial correlation. Accordingly, the position of an eyeor a pupil can correlate with a predefined or predetermined illuminationfunction.

According to a first exemplary embodiment in this regard, a plurality oflight sources could be used, the light of which is emitted in differentdirections. Accordingly, it is possible to illuminate the heads of aplurality of observers and the eyes from different directions. Thedifferent illumination directions may be switched on and off, namely forexample by switching light sources of different directions on and off.This may be done sequentially or simultaneously, for examplesequentially in the case of illumination with light with essentially thesame wavelength. If illumination light of different wavelengths is used,this could also be carried out simultaneously.

According to another exemplary embodiment in this regard, a scanningsolution could be used. In this case, a scan (raster) may for example becarried out in one direction or in two, three or more differentdirections. Each one-dimensional scan (i.e. each raster of a light beamalong an essentially rectilinear line) gives an increase in the retinareflection signal. Here as well, the use of a narrowband spectral filtermay be employed in order to separate the light source of the scannerfrom the ambient light and therefore increase the signal-to-noise ratioof the detected signal.

The evaluation or determination of the position of the eyes may becarried out sequentially, for example in two different directions.Accordingly, the x and y positions of the eye, or of the eye pupil, mayfor example be determined within 1/1000 of a second, when a CMOS linedetector is used.

It is furthermore possible to implement different scan methods. Forexample, global scans may be carried out, for example in the x and ydirections or in crossed directions. Angle-dependent scans may also beimplemented. Furthermore, an α and β angle scan may be used in order todetermine direction-dependent sections of the angle scanning lines. Aplurality of scanning methods may be combined, in order to reduce orexclude possible uncertainties in the position determination.

In addition to this, a scan region may be defined or established. Thisscan region may be substantially smaller than the overall scan region.

Accordingly, the scans may be carried out in these reduced scan regions,so that the scan speed and the eye detection can be carried out morerapidly.

Specifically, in one exemplary embodiment, a line scanner arranged inthe x direction, or in the horizontal direction, could be provided onone side of the display device and a linear detector or a(two-dimensional) detection matrix could be arranged on the other sideof the display device. It is furthermore possible to provide linescanners and detectors on both sides of the display device. A comparablearrangement may be provided on the upper and lower sides of the displaydevice, for example in order to implement a y scan.

A cost-efficient solution could, for example, be carried out in that aDOE (diffractive optical element) is arranged in front of an IR-LED(infrared light-emitting diode) and a one-dimensional scan mirror, theIR-LED and the one-dimensional scan mirror being arranged in a standardIC package which also contains all the electronic driving, in order todrive the small scanning mirror.

This detection principle could also be used in conjunction with an HMD(head-mounted display, a display adapted to an observer's head).

If, for example, one- or two-dimensional CMOS detector arrays are used,here again a restricted scan range may be selected so that signals canbe detected from the restricted scan range and read out with anincreased repetition rate. To this end, for example, it is possible touse a module for finding an observer's head, which only detects theposition of the observer's head. These position data of the observer'shead can then be used for the selected scan range, for example by usingtwo one-dimensional scanners.

For example, a small region of 25 mm×25 mm or even substantially lesscould be used, this region being centered approximately on the middle ofthe eye pupil. This region, or this surface, is illuminated with theone-dimensional or two-dimensional line scan. Fast photodetector diodesmay be arranged on the edge of the display device. These detectors mayfor example be provided with narrowband filters, which are tuned to theillumination wavelength—for example near-infrared light-emitting diodes.Accordingly, a rapid subsystem is thereby produced which can be used inthe display device specifically when the display device is configured inthe form of a direct-view device, an HMD or a mobile display or atablet. The photodetectors or photodiodes may also have a speciallytuned angle-dependent direction characteristic, which detect inparticular light from predetermined spatial regions or tracking regions.

In this way as well, the amount of light which does not come from thescan range, or the detection range, can be reduced.

According to another refinement of the apparatus, the apparatuscomprises a filter, which is arranged in front of the first camera andis transmissive essentially only for light of a first visible wavelengthand/or a second visible wavelength and/or a third visible wavelengthand/or infrared wavelength.

The associated advantages have already been described above withreference to the method according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further configurations will now be explained in more detail with the aidof the drawing. In the schematic drawing,

FIG. 1 shows a flow chart according to an exemplary embodiment of themeasurement method according to the invention,

FIG. 2 shows an apparatus for carrying out the measurement methodaccording to an exemplary embodiment according to the invention,

FIG. 3 shows, in a plane of the light source images, the position of theeyes of an observer relative to the light source images of theillumination light, the plane of the light source images in thisexemplary embodiment being arranged parallel to the surface of thecontrollable spatial light modulator,

FIG. 4 shows a plan view of an exemplary embodiment of the apparatus forcarrying out the measurement method according to the invention and theeyes of an observer, and

FIG. 5 shows the transmission characteristic of a triple bandpass filterin a diagrammatic representation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a flow chart according to an exemplary embodiment of themeasurement method according to the invention in a schematicrepresentation.

In a first step 1, an object is illuminated by predeterminedillumination by means of a display device, and a first location of anobject is marked by the intensity distribution of the illumination lightin a plane of a light source image.

In a second step 2, the relative position of the first location inrelation to a second location of the object is determined in acoordinate system of a camera.

FIG. 2 shows an exemplary embodiment of an apparatus 3 according to theinvention. The apparatus 3 comprises a display device 4, a camera 5 andan evaluation unit 6. The display device contains a light source 7, aspatial modulator for light 8 and an optical system 9.

If a light source of small extent is expanded onto a large area, whichis denoted by 7 in FIG. 2 , then an optical system which has a focusingeffect at least in one direction generates at least in one direction alight source image which, for example, lies close to the plane 13. If 7is a luminous surface, then in 13 there is an intensity distributionwhich is proportional to the plane wave spectrum of the luminoussurface. A spatial modulator may in this case introduce diffractionbroadening.

Spatial modulators for light 8 are also known by the term spatial lightmodulator, or the abbreviation SLM, and are used to impose a spatialmodulation on light. Typically, SLMs modulate the intensity of thelight. Nevertheless, SLMs which modulate the phase are also known, andit is furthermore conceivable to modulate the phase and the intensitysimultaneously with an SLM.

In the exemplary embodiment shown, the display device 4 is driven by theevaluation unit 6 via a connection 10 and the illumination with whichthe display device 4 illuminates an object 11 is predetermined. In thepresent case, the object 11 is an observer of the display device 4. Bymeans of the predetermined illumination, an intensity distribution ofthe illumination light 12 is generated in a plane of a light sourceimage 13, and a first location of the object 11 is thereby marked.

In general, the intensity distribution generated by the display devicein the plane 13 may be much smaller than in FIG. 2 . It may, forexample, involve a viewing window which has a dimension of 10 mm×10 mm,or even only a diameter of 3 mm.

With the camera 5, the intensity distribution of the illumination light12 in the plane of the light source image 13 is recorded and the firstlocation of the object is recorded with the camera 5. The camera 5likewise records a second location of the object 11, here the eye pupil14 of the observer. From the data provided by the camera 5 via theconnection 15, the evaluation unit 6 then determines the relativeposition of the first location in relation to the second location of theobject 11 in the coordinate system of the camera 5.

FIG. 3 shows the position of the eyes 16 and 17 of an observer, whoseface (not shown in FIG. 3 ) is illuminated by means of a display device(not shown in FIG. 3 ), in particular a holographic or autostereoscopicdisplay device. During the illumination of the observer with the displaydevice, the intensity distribution of the illumination light frequentlyhas light source images of a plurality of diffraction orders 18-30. FIG.3 shows diffraction orders 18-30 which were obtained by means oftwo-dimensional encoding and are represented as black circular areas.The undiffracted light source image 18 is denoted as the light sourceimage of the 0^(th) diffraction order. The region which comprises theundiffracted light source image 18, and extends as far as the closestlying light source images 19-22 of higher diffraction order, is referredto as the viewing window 31. The viewing window 31 is outlined as anellipse in FIG. 3 . Light source images lying further away from theviewing window 31 may, for example, be reduced in their intensity by acosinusoidally extending apodization profile of the pixels of thecontrollable spatial modulator, as described for example in WO2009/156191 A1. If, as shown in FIG. 3 , the viewing window 31 coincideswith the position of the eye 16, then the other light source images canbe suppressed to such an extent that they are no longer perceptible tothe other eye 17. So that this can be done even in the event of movementof the eyes, the illumination is typically adapted continuously to theposition of the eyes. The eye movements to be taken into account forthis are indicated by four short arrows in FIG. 3 .

FIG. 4 shows another exemplary embodiment of an apparatus 32 accordingto the invention. The apparatus 32 comprises a display device 33, twocameras 34, 35 and an evaluation unit 36. The orientation andpositioning of the two cameras 34, 35 in relation to the display device33 are predetermined in a fixed way by the mounting. In other words, thecoordinate systems of the two cameras 34, 35 are calibrated.

The space in front of the apparatus 32, in which the observer islocated, is recorded by the two cameras 34, 35, the face of the observerbeing recognized with the aid of the camera images. The position of theeye pupils 37, 38 is determined in the calibrated coordinate system ofthe respective camera 34, 35. In this way, two direction vectors 39, 40are first obtained for the eye pupil 37, which extend from the positionof the cameras 34, 35 and point in the direction of the eye pupil 37.From the point of intersection of the straight lines spanning the twodirection vectors 39, 40, it is then possible to determine the distanceof the eye pupil 37 from the display device 33, or the relative positionbetween the eye pupil 37 and the display device 33. The same procedureis carried out with the second eye pupil 37.

During transport of the apparatus 32, it may occur that the position ofthe cameras 34, 35 or their orientation with respect to the displaydevice 33 is unintentionally altered. The coordinate system thereof istherefore no longer calibrated in relation to the display device 33.

The distances of the light source images generated on an object (cf.FIG. 3 ) may be predetermined in a fixed way by the native pixel rasterof the display device 33, e.g. as a Fourier transform of thecontrollable spatial light modulator, in particular when a displaydevice according to WO 2006/066919 A1 is used, or the measurement methodaccording to the invention is applied to a display device as disclosedin WO 2006/066919 A1. For calibration of the device 32, the light sourceimages of a plurality of diffraction orders 18-30, that is to say thelight source image raster, may be recorded with the respective camera34, 35, and the position of the object may be determined from therelative position of the light source images in the respectivecoordinate system of the camera 34, 35. Since the position of the lightsource images in relation to the display device 33 is known, theapparatus can therefore be recalibrated.

The invention claimed is:
 1. A measurement method for determining adistance of a light intensity distribution to an object comprising:generating the light intensity distribution in a light source imageplane, in which the object is located, by a display device through aviewing window, where the light intensity distribution in the lightsource image plane comprises a light source image, wherein the lightintensity distribution is brought to coincide with a predeterminableregion of the face of the observer, in particular with the eye pupil ofthe observer, recording the generated light intensity distribution andthe object by a camera, and determining from data provided by the camerathe distance of the generated light intensity distribution to the objectby an evaluation unit.
 2. The measurement method as claimed in claim 1,wherein the intensity distribution in the light source image planecomprises a light source image of a diffraction order.
 3. Themeasurement method as claimed in claim 1, wherein the object is anobserver, and the distance of the light intensity distribution to theobserver is determined in a coordinate system of the camera.
 4. Themeasurement method as claimed in claim 1, wherein the light intensitydistribution is brought to coincide with the predeterminable region ofthe face of the observer, in particular with the eye pupil of theobserver, by variation of an illumination provided by the displaydevice.
 5. The measurement method as claimed in claim 1, wherein thelocation of the object is defined by illumination provided by thedisplay device with a second intensity distribution in a second lightsource image plane.
 6. The measurement method as claimed in claim 5,wherein a predeterminable pattern is formed on the object, in particularthe face of the observer, with the first and second intensitydistributions, where an image of the pattern is recorded with thecamera, and where the recorded image of the pattern is examined fordifferences from the predeterminable pattern.
 7. The measurement methodas claimed in claim 5, wherein a first diffraction order is used as thefirst light source image and a different diffraction order is used asthe second light source image.
 8. The measurement method as claimed inclaim 1, wherein a calibrated object is used.
 9. The measurement methodas claimed in claim 5, wherein a coordinate system of the camera iscalibrated in relation to a coordinate system of the display device fromthe relative position of the light intensity distribution to the objectin the coordinate system of the camera.
 10. The measurement method asclaimed in claim 1, wherein the camera is arranged in at least one of:at a predetermined distance and in a predetermined orientation, withrespect to the display device, and wherein the position of the object ina coordinate system of the display device is determined from thedistance of the light intensity distribution to the object in thecoordinate system of the camera.
 11. The measurement method as claimedin claim 1, wherein at least one of the first light source image and thesecond light source image is generated by the optical system of thedisplay device and by illumination of a controllable spatial lightmodulator with light of at least one of a first visible wavelength and asecond visible wavelength and a third visible wavelength and an infraredwavelength, and wherein at least one of the camera and a further camerais provided with a filter which is transmissive essentially only forlight of at least one of the first visible wavelength and the secondvisible wavelength and the third visible wavelength and infraredwavelengths.
 12. The measurement method as claimed claim 1, wherein thedistance of the light intensity distribution to the object is determinedin a second coordinate system of a second camera.
 13. The measurementmethod as claimed in claim 4, wherein the distance of the lightintensity distribution to the eye pupil of the observer is determined inthe coordinate system of the camera, wherein the light intensitydistribution is brought to coincide with a predeterminable region of theface of the observer, in particular with the eye pupil of the observer,by variation of the illumination provided by the display device.
 14. Themeasurement method as claimed in claim 1, wherein the light intensitydistribution is brought to coincide with the predeterminable region ofthe face of the observer, in particular with the eye pupil of theobserver, by variation of an illumination generated by the displaydevice by constructive or destructive interference of coherent lightbeams.
 15. An apparatus for carrying out a measurement for determining adistance of a light intensity distribution to an object, wherein theapparatus is adapted and configured to: generate a light intensitydistribution in a light source image plane, in which the object islocated, by a display device through a viewing window, where the lightintensity distribution in the light source image plane comprises a lightsource image, wherein the light intensity distribution is brought tocoincide with a predeterminable region of the face of the observer, inparticular with the eye pupil of the observer, record the generatedlight intensity distribution and the object by a camera, and determinefrom data provided by the camera the distance of the generated lightintensity distribution to the object by an evaluation unit, wherein theapparatus comprises the display device, at least one camera and theevaluation unit.
 16. The apparatus as claimed in claim 15, wherein thecamera comprises a CCD sensor or a CMOS sensor or wherein the camera isa color camera.
 17. The apparatus as claimed in claim 15, whichcomprises a light source, where an intensity distribution in a lightsource image plane can be generated with the light source and theoptical system.
 18. The apparatus as claimed in claim 15, wherein theapparatus comprises a filter, wherein the filter is arranged in front ofthe camera, and wherein the filter is transmissive essentially only forlight of at least one of a first visible wavelength and a second visiblewavelength and a third visible wavelength and infrared wavelength.